This invention relates in general to protective fuse assemblies for liquid-cooled transformers. More particularly, the invention relates to a sealing mechanism to prevent oil from escaping the confines of a transformer tank when a submerged, bayonet-type circuit breaker or fuse is removed from a transformer tank. The bayonet-style fuse is designed to operate under oil and be easily replaceable after operation. The fuse serves to protect an electrical system from overload or transformer failure resulting in a short circuit. In this type device, a fuse is inserted into a tubular housing mounted in a tank and having a pair of contacts in its bottom, lower end. The fuse is installed by attaching it to one end of a fuse holder which is then pushed through the opening in the transformer tank wall and into the fuse housing until the fuse is submerged in oil between the two contacts. The opposite end of the fuse holder seals the top opening in the fuse housing. After the fuse has operated, the fuse and holder are withdrawn from the housing and a new fuse is attached to the holder and inserted.
While the forgoing design allows quick removal of the fuse, it requires the air-oil interface to be well below the tank wall opening to prevent oil from draining through the tank wall opening in the fuse housing as the fuse and holder are withdrawn. Even with the air-oil interface below the tank wall opening, certain factors like heat and pad-tilt can cause the oil level to rise to a point above the opening in the tank wall. For example, on larger pad-mounted transformers, temperature induced oil height variations cause the oil level to fluctuate between -2.63" and +3.25" on a 72" high tank. In addition, a pad-tilt of 2 or 3 degrees can shift the oil height an additional 1" on a 40" deep (front to back) tank. When the fuse is removed while the oil height is elevated, oil escapes from the fuse housing opening causing contamination of the transformer oil and possible damage to rubber termination systems mounted onto the transformer front plate.
Another, more critical problem arises when the oil level becomes too low causing the top contact of the fuse to be exposed to air. This causes a danger for personnel removing the fuse as an arc between the upper contact and the transformer wall can result.
There is a need therefore, for a sealing system for use with a bayonet-style fuse assemblies wherein the fluid level of transformer oil can be kept well above the fuse contacts without concern of oil escaping through the tank wall as the fuse is withdrawn.